New Castle County, DE Accessory Structures: ADU Rental Restrictions (2026)
Key Facts
- ADUs allowed
- One per single-family detached lot
- Occupancy rule
- Owner must live in home or ADU
- Rental limit
- Only one unit rentable at a time
- Registration
- Required under Chapter 19 before occupancy
- Scope
- Unincorporated county plus opt-in municipalities
Summary
New Castle County caps ADU rentals at one unit per lot, requires owner-occupancy of the principal home or ADU, and makes rental ADUs register under Chapter 19 before occupancy.
Once an ADU is established, the primary structure shall not be used for apartment conversion and only one (1) of the dwelling units may be rented. ... Rental code registration. If the ADU is to be rented and prior to the issuance of a certificate of occupancy, the property owner shall register the ADU pursuant to the requirements of Chapter 19.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 5).
Full Breakdown
Under UDC Sec. 40.03.410(I), a single-family detached lot can add one accessory dwelling unit, but the property owner must live in either the principal house or the ADU as a legal residence, and only one of the two units can ever be rented -- converting the primary house into a second apartment is barred. If the ADU is rented, the owner must register it under Chapter 19's Residential Rental Property Registration System before a certificate of occupancy issues. Chapter 19 covers unincorporated New Castle County plus incorporated municipalities that have signed a participation agreement; Wilmington and Newark run their own separate municipal codes and are not covered by this chapter.
Violations & Fines
Renting an ADU without Chapter 19 registration draws a $200 administrative penalty plus $15 per day per unregistered unit, and repeat rental-code convictions can reach $5,000 in criminal fines.
Frequently Asked Questions
Can I rent out my New Castle County ADU?
Does Wilmington or Newark follow this ADU rule?
What happens if I don't register a rented ADU?
Sources & Official References
Other rules in New Castle County
Compare New Castle County to another location·View the Delaware accessory structures overview
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